We have a plan which looks for inconsistency in input file such as nulls, value out of range, invalid values and etc. In case, if plan finds-out any such inconsistency we want to fail the plan or fail the workflow with error message.

Is there any function to fail the plan?
Is there any option fail workflow in such case?

Yes. You can include run shell script (or windows command) step in your workflow and make it return error code in case of inconsistent data. In that case this step would be considered FINISHED_FAILURE and so the whole workflow.